Field choppers or forage harvesters generally comprise a vehicle structure which can be drawn over the field by a tractor or may be self-propelled, and is provided with a crop pickup device for drawing a standing crop or a previously cut crop into the region of a blade drum or reel in which the crop material is comminuted and from which it is blown into a silage wagon or other transport unit associated with the harvester. From the wagon, chopped crop material may be used for direct feeding in animal husbandry or stored in a silo.
Field harvesters of this type may be used for grasses and leguminous crops by providing the crop pickup device with an apron having a mower blade at its leading edge and a batten arrangement for advancing the crop material onto this apron. Alternatively, the leading edge of the apron may be provided with pickup tines for lifting a previously mown crop material from the ground. The apron may be a conveyor belt, a large-diameter drum or a series of rollers or drums capable of advancing the crop material into the throat of the machine and toward the blade reel or drum.
Such forage harvesters and field choppers can also be used to comminute stalk crops, such as corn, and other upstanding row crops by providing the pickup with guides which run along the rows and cause the stalks to be engaged by chains or the like lifting the crop material into the throat of the machine and toward the cutter blades. Further cutters may be provided to sever the stalks at or just above ground level.
Various drive systems for such machines have been provided heretofore and, for example, they may make use of a power takeoff from the towing tractor or a self-contained prime mover and generally include a motion-distributing system for operating the various moving elements of the crop pickup and intake device. For example, between the crop pickup and the blade drum there may be provided one or more textured, toothed or even smooth rollers which facilitate advance of the crop material toward the blade drum.
It has also been proposed to provide means for reversing the sense of rotation of the pressing or crushing rollers of the crop-advance system, ahead of the blade drum or reel to enable obstructions to be cleared in a convenient manner. It is important that the blade drum or reel continue to rotate in its normal sense during such clearing operations. However, the blade drum should be rotated in the reverse or opposite sense for grinding and sharpening.
A reversal of the sense of rotation of the intake or crop-advance rollers has been described in German published application (Offenlegungsschrift) 20 11 420 (U.S. Pat. No. 3,730,037) in the form of a belt and friction wheel transmission. The belt and friction wheel transmission is provided with multistep sheaves spanned by a V-belt so that the multistep sheaves are driven in the same sense. Friction wheels are provided on the shafts and along the axes of these sheaves and, upon reduction of the interaxial spacing, peripherally engage with frictional contact to rotate the driven wheel and its sheave and shaft in the sense opposite that of the driving wheel, sheave and shaft, the belt being loosened and incapable of motion transfer in the slack condition brought about by reduction of the interaxial spacing.
A significant disadvantage of this system is that the driven shaft of this belt and friction wheel transmission is connected by chain drives with the pickup and advancing rollers. Such chain drives are particularly prone to damage because of accumulation of contaminants and wear and require continuous attention and repair. Furthermore, the chain drives obstruct access to the crop-advance rollers and the crushing or pressing rollers as well as adjustment of the blades of the machine.